The subject matter disclosed herein relates to turbines. Specifically, the subject matter disclosed herein relates to seals in gas turbines.
The main gas-flow path in a gas turbine commonly includes the operational components of a compressor inlet, a compressor, a turbine and a gas outflow. There are also secondary flows that are used to cool the various heated components of the turbine. Mixing of these flows and gas leakage in general, from or into the gas-flow path, is detrimental to turbine performance.
The operational components of a gas turbine are contained in a casing. The turbine is commonly surrounded annularly by adjacent arcuate components. As used herein, the term “arcuate” may refer to a member, component, part, etc. having a curved or partially curved shape. The adjacent arcuate components include outer shrouds, inner shrouds, nozzle blocks, and diaphragms. The arcuate components may provide a container for the gas-flow path in addition to the casing alone. The arcuate components may secure other components of the turbine and may define spaces within the turbine.
Between each adjacent pair of arcuate components is a space or gap that permits the arcuate components to expand as the operation of the gas turbine forces the arcuate components to expand. Typically, one or more seal slots are defined on the end faces of each arcuate component for receiving a seal assembly in cooperation with an adjacent seal slot of an adjacent arcuate component. The seal assembly is placed in the seal slot to prevent leakage between the areas of the turbine on either side of the seal assembly. The conventional static seals used are either separate laminate or solid seals.
In some embodiments, the seal slot may include multiple seal slots within the end of a particular arcuate component that connect one to another. Furthermore, multiple seal slots within the end of a particular arcuate component may be angled in orientation to each other. Typically a planar seal is received in each of the seal slots that are connected. Each of the planar seals has ends, with the seals being positioned in each of the two seal slots in an end-to-end orientation.
In advanced gas path (AGP) heat transfer design for gas turbine engines, the arcuate components, and in particular the shrouds, are fabricated with ceramic matrix composites (CMCs). The static seals in the AGP shrouds are made of a high temperature nickel alloy. As the CMC shrouds have lower co-efficient of thermal expansion (CTE) compared to the static seals, the seals have to be designed shorter to account for the CTE mismatch. Typically, a plurality of vertical solid laminate/solid seals are designed shorter and are susceptible to shifting downward within the seal slot and a bottom horizontal seal while under-going thermal expansion would eventually crush the vertical seals.
Accordingly, it would be desirable to reduce or substantially eliminate leakage between AGP turbomachinery components formed of ceramic matrix composites, such as between adjacent shrouds, by utilizing seals. It is further desirable that such seals are designed to account for CTE mismatch between the AGP components and the seal, while being substantially temperature resistant and wear resistant (i.e., long component life), sufficiently flexible so as to provide adequate sealing during use and any misalignment, and meet the manufacturing, assembly, installation and robustness requirements associated with turbomachinery.